Wireless communications systems are operated worldwide by wireless carriers who offer services such as interconnect, short message service (SMS), packet data and push-to-talk. Each wireless communications system services subscribers within a coverage area and operates using one or more wireless technologies such as code division multiple access (CDMA), global system for mobile communication (GSM), time division multiple access (TDMA) or Advanced Mobile Phone Service (AMPS).
PTT services (also known as a walkie-talkie or dispatch services) are currently offered by some wireless carriers, such as Nextel's Direct Connect® service offered on an Integrated Digital Enhanced Network (iDEN), and new PTT services and technologies have been proposed, including dispatch to desktop (D2D), selective dynamic group call (SDGC) and private call (PC) services. Generally, a PTT call provides near-instant, half-duplex communication between a PTT caller and a target group of PTT users. In today's systems, subscribers on a network operated by a first wireless carrier cannot always engage in PTT calls with PTT subscribers on a network operated by a second wireless carrier. When subscribers are roaming globally, and may connect to wireless carriers operating on different technologies, some concerns includes call set up delays, number of control messages, and call loss rates due to inter-system roaming.
Accordingly, a need exists for an inter-system network that is optimized for PTT and other wireless communications among subscribers on different carrier networks, irrespective of subscriber and carrier location and underlying PTT technology.